The invention relates generally to subsurface well treating apparatus and operations. In particular, the invention relates to an injection mandrel and method for circulating well treating fluids into subsurface wells to treat produced fluids from subsurface earth formations.
In order to complete oil and gas wells, subsurface earth formations are perforated to bring the wells into production. The fluids produced may subject the subsurface and surface equipment to corrosion from a variety of chemical agents present in the fluids. To combat this corrosion, a number of well-known corrosion inhibitors may be circulated through the wellbore to reduce or prevent the undesirable effects of the corrosive agents.
Produced fluids also may contain salts and other dissolved and undissolved solids which can precipitate and deposit on the surface of the production tubing or in the perforations in the subsurface earth formation. As deposits build, production flow becomes restricted. To combat this problem, one or more of a number of well-known solvents may be circulated through the well to dissolve any flow restricting deposits and to prevent deposits from recurring.
Apparatus and methods are known to circulate such treating fluids through wells at various depths in the wells. Side-pocket mandrels may be utilized for this purpose. A treating fluid is injected into the annulus of a well above a packer assembly, through ports in the side-pocket of the mandrel, through a chemical injection valve set in the side-pocket, and into contact with the produced fluids flowing out of the well. Once the fluids have been treated, they flow through the mandrel and production tubing to the surface for recovery.
Side-pocket mandrels suffer from several shortcomings when used for the above purpose. First, side-pocket mandrels require complicated kickover tools to set and retrieve chemical injection valves in their side valve pocket. Current kickover tools require involved wireline operations which are typically not practical at depths below about 15,000 feet. Second, the construction of a side-pocket mandrel does not permit circulation of the treating fluid below the packer assembly because the mandrel does not extend below the packer. Third, side-pocket mandrels allow untreated, often corrosive, produced fluids into the upper annulus of the well above the packer assembly when the chemical injection valve is not in place. In the annulus, such produced fluids could damage the tubing, casing and other equipment, such as a subsurface safety valve.
Other designs have also been proposed, but these designs suffer from the same or other shortcomings. The other shortcomings include limitations on the ability to circulate treating fluids at any desired depth in a well, limitations on conducting perforating, logging or other operations without having to pull the mandrel from the well, and limitations on flow through the mandrel, which may cause pressure losses and erosion problems.
Ideally, an apparatus for treating produced fluids in a wellbore will have the following characteristics. The annulus, the space between the production tubing and the casing, above the packer should be effectively isolated from produced fluids. The apparatus should be capable of circulating treating fluids across the perforations or at any other preselected depth. The apparatus should be capable of being routinely set and operated at total depths in excess of 15,0090 ft. There should be a capability for conducting workover operations through the apparatus. Restrictions to flow should be minimized.